Since polyimide film has light weight and is excellent in various properties, for example, flexibility, film strength and heat resistance, there has been used in various field, particularly in electronic/electrical field as materials for flexible printed wiring board and COF substrate.
As a general manufacturing method of a polyimide film, there is known a method including casting onto a support a solution of a polyimide precursor such as polyamic acid in a solvent to obtain a self-supporting film (also referred as gel-like film or gel film) and performing heating it at 300° C. to 500° C. while holding both ends of the self-supporting film (also called as thermal cure). For imidizatyion, chemical imidization, thermal imidization, and a reaction using the both are employed. For example, methods of producing film mainly utilizing thermal imidization and/or chemical imidization are disclosed in JP-A-2009-67042 (patent document 1), JP-A-2003-268133 (patent document 2). JP-A-2000-204178 (patent document 3)
Depending on the method of the imidization (thermal imidization or chemical imidization) as well as the difference of raw materials such as tetracarboxylic acid component and diamine component, imidization ratio and solvent content of self-supporting film are appropriately determined and also the final heat treatment condition is appropriately determined. Finally, imidization is completed by the heat treatment (thermal cure) where the solvent is also removed and polyimide is obtained.
Since the volume of the self-supporting film is reduced during the heating of the self-supporting film, heating is performed while the both ends of the film are held for the stable manufacturing of the film. If necessary, the width between the both ends may be enlarged for stretching or the width between the both ends may be reduced to allow shrinking (relaxation of stress). The holding of the both edge of the film is performed by, for example, method of holding by piercing the edge of the self-supporting film with a plurality of piercing pins (pin-type tenter), method of grasping the edge of the self-supporting film (clip-type tenter or chuck-type tenter). The tenter apparatus is not only used for the polyimide, but also widely used for the other films.
A conventional tenter apparatus has a structure in which a tenter chain is moved on a roller within a tenter rail as described in Japanese Patent Laid-Open No. 2001-146344 (Patent Document 4).
In the following, the tenter apparatus disclosed in Patent Document 4 is described with reference to FIG. 12 which is a section view showing a tenter rail and a tenter chain on one side. As shown in FIG. 12, tenter rail 140 has support walls 141 placed at an interval between them and chain support roller 142 supported rotatably between support walls 141. Tenter chain 150 is placed between support walls 141 and is supported on chain support roller 142.
Tenter chain 150 is formed by alternately coupling an inner link having a pair of inner plates 151a and 151b with an outer link having a pair of outer plates 154a and 154b through coupling pin 155. The inner link also has rollers 153a and 153b into which coupling pin 155 is inserted through a bush (not shown). Rollers 153a and 153b are placed in an axial direction of coupling pin 155 and can be rotated individually relative to coupling pin 155.
Tenter chain 150 is used in an orientation in which outer plates 154a and 154b are opposite to each other in a vertical direction. Thus, in use, outer plate 154b located on the lower side is supported on chain support roller 142.
Outer plate 154a located on the upper side in use is bent in a crank shape and extends in a transverse direction. Pin plate 164 having a plurality of piercing pins 165 is attached to an end portion of outer plate 154a. Film F is held such that its edge portion is pierced with piercing pins 165, and in this state, tenter chain 150 is moved to carry film F.
When this apparatus is used for manufacturing a polyimide film, an extremely large tension is applied to the tenter chain 150 in the transverse direction (direction indicated by arrow A in FIG. 12) due to stretching performed with an enlargement/reduction function of the tenter rail as well as a volume shrinkage of a self-supporting film, so that tenter chain 150 is moved in an inclined state. The inclination of tenter chain 150 causes roller 153a on the upper side to come into contact with support wall 141 on the inner side and causes roller 153b on the lower side to come into contact with support wall 141 on the outer side. Since the movement of tenter chain 150 in this state allows rollers 153a and 153b to be rotated in opposite directions, the rotation of the rollers is not prevented even when tenter chain 150 is inclined.